Loud-speaker



L. LEVY LOUD SPEAKER Dec. 10, 1929.

Filed 001:. 1. 192a v l/lllbl' Patented Dec. 10, 1929 PATENT OFFICE LUCIEN Law, or rams, Eamon Loon-SPEAKER Application filed October 1, 1928, Serial No.- 309,425, and in France October 4, 1927.

My invention relates to improvements in loud-speakers. Instruments so-called loudspeakers have already been proposed for converting electric energy having an audible frequency into audible energy and inversely. Said instruments comprise essentially an electric motor which converts alternate electric energy into oscillatory mechanical energy and a diaphragm designed to receive at certain points of its surface the oscillatory mechanical energy which propagates on the surface of the diaphragm and is transmitted in part to the air particles in contact with the diaphragm.

In loud speakers the diaphragm is frequently made of metal and is of reduced di-.

mensions, but it is frequently embedded and capable of vibrating itself. On the other hand the sound horn is capable of sounding under the action of certain acoustic vibrations. The result of the above phenomena is that the loud speaker has an efliciency acoustic energy emitted p electric energy supplied 'It will also be noted that at a glven mo- Y ment, owing to the propagation of the elastic wave, the various parts of the diaphragm ac quire different speeds which may even be of opposite direction at points located at various distances from. the center of commotion;

"consequently one part of the diaphragm radiates in an opposite direction to that of another part thus creatingcurrents of acoustic circulation which possess'no radiating energy and produce losses of energy.

Lastly at certain points of the diaphragm the vibratory energy is of such a nature that surface.

it may be integrally radiated in the surrounding atmosphere, said points are those at which the vibratory energy of the diaphragm per cm for a given amplitude V is equal to the vibratory energy that the surrounding air may carry (given for instance by Wiens formula) U, amplitude specific heat at confrequency stant pressure and constant volume Briefly stated, the emission of energy by means of a diffuser is a complex phenomenon V speed of sound} which baffles all reliable calculations, which produces great losses of energy, it requires in fact much larger surfaces than those which would be necessary if all parts of the radiatlng surface were rationally utilized and which owing to thenon-radiation of the whole enrgy existing at every point produces.

resonance phenomena.

My invention relates to improvements in acoustic radlating surfaces with the ob ect of producing:

1st, a good radiating energy per cm of the 2nd, a continuous radiation at all frequencies.

3rd, the absence of all resonance phenomcna. I

According to my invention instead of utilizing the radiating diaphragm as wave transmitting surface (this being the case when vibratory mechanical energy is applied at one point of said diaphragm) it is specialized in its radiating function: 1st by the application of mechanical energy at numerous points vibrating in phase or approximately; 2nd by equalizing the vibratory energy applied to the diaphragm for a given frequency and amplitude to the energy which it can radiate for the same amplitude at the same fre-,

quency; showing thus that when this uniformit is obtained for a given frequency it is o tained for all frequencies provided that the 1st condition is fulfilled; the uniformity is obtained by providing the motor with a lever device the ratio of which may be regulated in order to act upon the transmitter; 3rd by interposing between the motor which delivers the vibratory energy and the radiating diaphragm one or more surfaces for the propagation of elastic waves designed to connect the motor with the various points of the diaphragm by giving them motions which are substantially in phase.

The diaphragm may be made of any appropriate light substance which does not propagate the elastic waves, such as rubber, goldbeaters skin, material, cellulose acetate, paper, etc.

The waves propagating surface should be such that the propagation speed will be as high as possible in order that the phase displacement may be as slight as possible between the various points of the diaphragm. Consequently it will be made preferably of metal such as duralumin when the propagation speed is about 5000 meters per second.

Thus in the case of 5000 periods the wave length is approximately 1 meter and in that of a loud speaker having a radius of about 25cm the phase displacement between two points on the diaphragm is less than period and may be moreover reduced at will.

The invention will be better understood by reference to the accompanying drawing in which Fig. 1 represents a loud speaker diaphragm constructed according to my invention.

Referring to the drawing, Fig. 1 designates the motor operating the wave propagating surface which is composed of a series of triangular shaped metal blades 2 soldered together provided with a circular foot 3, Figs. 2 and 3, formingtogether equal dihedrons.

Fig. 2 is a rear view of the diaphragm;

Fig. 3 shows a single blade for connecting the motor to the diaphragm.

A radiating diaphragm 4 of material, rubber, paper, etc., in the shape of a spherical cap is stretched over the feet 3. It is preferably contained in a casing 5 to which it is connected by means of an elastic joint 6 which prevents the circulating'currents passing between the front and the back surface of the radiating diaphragm 4.

The feet 3 of the blades may be connected together by means of a wire netting 8.

The mode of operation is as follows:

The mechanical vibrations produced by the motor are transmitted to the blades at the point 7. They produce elastic waves in said lades which transmit synchronous motions to every point of the feet 3 and consequently to every point of the diaphragm.

All the improvements as aheve described may apply indifi'erently to the operation with a loud speaker or with a receiving microphone.

What I claim and desire to-secure by Letters Patent of the United States is:

1. In a loud speaker, a radiating membrane that does not propagate waves, and a wave propagating surface connected to the rear of the membrance along lines whose points vibrate in phase.

2. in a loud speaker, a radiating membrane that does not propagate waves and having spehircal form, and a propagating surface of radial orthogonal blades symmetrically disposed about the axis of the membrane, the lines of contact of the blades with the membrane being along curves all of whose points vibrate in phase.

3 In a loud speaker, a spherical paper membrane, and a wave propagating means connected thereto, said means consisting of radial metallic vanes connected orthogonally to the membrane and regularly disposed about its axis and having curved lines of contact with the membrane all of whose points vibrate in phase.

In testimony that I claim the foregoing as my invention I have signed my name.

LUCIEN LEVY. 

